Transducer temperature sensing

ABSTRACT

In described examples, one or more devices include: apparatus including a lens element and a transducer to vibrate the lens element at an operating frequency when operating in an activated state; and controller circuitry. The controller circuitry is arranged to measure an impedance of the apparatus, to determine an estimated temperature of the apparatus in response to the measured impedance, to compare the estimated temperature against a temperature threshold for delineating an operating temperature range of the apparatus, and to toggle an activation state of the transducer in response to comparing the estimated temperature against the temperature threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/887,923, filed Feb. 2, 2018, which claims the priority of U.S.Provisional Patent Application No. 62/454,149, filed Feb. 3, 2017, whichis incorporated herein by reference in its entirety.

BACKGROUND

Electronic optical sensors are widely used for generating electronicimages. Often, such sensors (e.g., “cameras”) are located in placesremote to a viewer. The remote locations include places (e.g., externalto vehicles) where contaminants (e.g. moisture and/or dirt) from theenvironment can cloud or otherwise obscure the camera lens, such thatdegraded images are generated by a camera having an obscured lens. Thedegradation of the image quality can decrease safety or security in manyapplications. Various techniques for automatically cleaning the cameralenses include water sprayers, mechanical wipers, or air jet solutions.Such approaches are not practical or too costly in a variety ofapplications.

SUMMARY

In described examples, one or more devices include: an apparatusincluding a lens element and a transducer to vibrate the lens element atan operating frequency when operating in an activated state, andcontroller circuitry. The controller circuitry is arranged to measure animpedance of the apparatus, to determine an estimated temperature of theapparatus in response to the measured impedance, to compare theestimated temperature against a temperature threshold for delineating anoperating temperature range of the apparatus, and to toggle anactivation state of the transducer in response to comparing theestimated temperature against the temperature threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example computing device 100 forcontrolling a transducer coupled to a lens element.

FIG. 2 is a cross-section view of an example camera lens cover system.

FIG. 3 is a waveform diagram of an impedance response of an examplecamera lens cover system over a broad frequency range.

FIG. 4 is a waveform diagram of an impedance response of an examplecamera lens cover system over a reduced frequency range.

FIG. 5 is a plot diagram showing a linear relationship between theimpedance response of an example camera lens cover system and operatingtemperatures thereof while operating at a selected operating frequencyof 20 kHz.

FIG. 6 is a flow diagram of an example process for estimating atemperature of an example camera lens cover system in response to animpedance measurement of the example camera lens cover system.

FIG. 7 is an isometric view of an example camera lens cover system.

FIG. 8 is an external view of example foreign contaminant volumes for anexample camera lens cover system.

FIG. 9 is a block diagram of an example signal generator of an examplecamera lens cover system.

FIG. 10 is a flow diagram illustrating an example method of foreigncontaminant removal from an exposed surface of the example camera lenscover system.

FIG. 11 is a top view of an example vehicle including example cameralens cover systems.

DETAILED DESCRIPTION

In this description: (a) the term “portion” means an entire portion or aportion that is less than the entire portion; (b) the term “housing”means a package or a sealed subassembly/assembly, which can includecontrol circuitry, a transducer, lenses and an imaging sensor in a localenvironment that is sealed from an outside environment.

Ultrasonic vibration of lens surfaces (including lens covers) of camerasystems (e.g. automotive systems including rear view and/or surroundview systems) can be more cost effective than various water sprayer,mechanical wiper, or air jet solutions. As described herein,piezoelectric transducers (e.g., within a camera housing) can bemonitored in a feedback loop structure without including a thermocouplein the feedback loop. The piezoelectric transducer is controlled byestimating a temperature of the piezoelectric transducer, such that, forexample, the buildup of heat (which can be caused by activating thepiezoelectric transducer) is limited by a comparison to a temperaturethreshold. The limiting of the buildup of heat helps prevent thepermanent depolarization of the piezoelectric transducer (e.g., whichcould adversely affect the ability of the piezoelectric transducer tovibrate).

The apparatus and methods described herein for controlling and operatinga piezoelectric transducer can help ensure that the temperature of thepiezoelectric transducer does not reach more than one-half a Curietemperature (in degrees Celsius) of the piezo material of the transducerbeing controlled. In example embodiments, the transducer lifetime can beextended by the avoidance of operating the piezoelectric transducer atpotentially damaging temperatures.

FIG. 1 is a block diagram of a computing device 100 for controlling atransducer coupled to a lens element. For example, the computing device100 is or is incorporated into, or is coupled (e.g., connected) to anelectronic system 129, such as a computer, electronics control “box” ordisplay, controllers (including wireless transmitters or receivers), orany type of electronic system operable to process information.

In example systems, a computing device 100 includes a megacell or asystem-on-chip (SoC) that includes control logic such as a centralprocessing unit (CPU) 112, a storage 114 (e.g., random access memory(RAM)) and a power supply 110. For example, the CPU 112 can be a complexinstruction set computer (CISC)-type CPU, reduced instruction setcomputer (RISC)-type CPU, microcontroller unit (MCU), or digital signalprocessor (DSP). The storage 114 (which can be memory such ason-processor cache, off-processor cache, RAM, flash memory, or diskstorage) stores one or more software applications 130 (e.g., embeddedapplications) that, when executed by the CPU 112, perform any suitablefunction associated with the computing device 100. The processor isarranged to execute code (e.g., firmware instructions and/or softwareinstructions) for transforming the processor into a special-purposemachine having the structures—and the capability of performing theoperations—described herein.

The CPU 112 includes memory and logic circuits that store informationthat is frequently accessed from the storage 114. The computing device100 can be controlled by a user operating a UI (user interface) 116,which provides output to and receives input from the user during theexecution the software application 130. The UI output can includeindicators such as the display 118, indicator lights, a speaker, andvibrations. The UI input can include sensors for receiving audio and/orlight (using, for example, voice or image recognition), and can includeelectrical and/or mechanical devices such as keypads, switches,proximity detectors, gyros, and accelerometers. For example, the UI canbe responsive to a vehicle operator command to clear an exterior surfaceof a backup camera of the vehicle.

The CPU 112 and the power supply 110 are coupled to I/O (Input-Output)port 128, which provides an interface that is configured to receiveinput from (and/or provide output to) networked devices 131. Thenetworked devices 131 can include any device (including test equipment)capable of point-to-point and/or networked communications with thecomputing device 100. The computing device 100 can be coupled toperipherals and/or computing devices, including tangible, non-transitorymedia (such as flash memory) and/or cabled or wireless media. These andother such input and output devices can be selectively coupled to thecomputing device 100 by external devices using wireless or cabledconnections. The storage 114 is accessible, for example, by thenetworked devices 131. The CPU 112, storage 114, and power supply 110are also optionally coupled to an external power source (not shown),which is configured to receive power from a power source (such as abattery, solar cell, “live” power cord, inductive field, fuel cell,capacitor, and energy storage devices).

The transducer controller 138 includes control and signaling circuitrycomponents for resonating a transducer of the lens cover system 132,such that the lens element can be cleaned by expelling foreign material(e.g., shaken clean of moisture). As described hereinbelow, thetransducer controller 138 includes a temperature calculator 140 fordetermining a temperature of the lens cover system 132, such that, forexample, the transducer of the lens cover system 132 is operated withina safe range of operating parameters.

FIG. 2 is a cross-section view of an example camera lens cover system.The camera lens cover system 200 generally includes a lens element 220,a seal 230, a housing 240, a transducer 250, and a camera 260. Thecamera 260 includes a camera lens 262, a camera base 264, aphotodetector 272, and controller circuitry 274. The transducer 250 isoperable to vibrate at a selected frequency (such as a factory-selectedfrequency or an operator-selected frequency) for motivating thedispersal of the moisture 210 (or other foreign materials) from theexterior (e.g., upper) surface of the lens element 220.

The lens element 220 is a transparent element elastically captivated ina distal (e.g., upper) portion of the housing 240. The lens element 220is arranged to receive light from surrounding areas and to opticallycouple the received light to the photodetector 272 (e.g., via the cameralens 262). The lens element 220 is arranged to protect the camera lens262 against moisture 210 intrusion, for example. The moisture 210 can bein the form of frost, water drops, and/or a film of condensation.Foreign materials (such as the moisture 210 and dirt particles) canblock and/or diffuse light, such that at least some of the receivedlight is prevented from reaching the camera lens (e.g., compound lens)262. In an embodiment, the lens element 220 can be a focusing lens(e.g., for refractively focusing light).

A seal 230 (such as a rubber seal) is arranged to elastically captivatethe lens element 220 to the housing 240 and to seal a cavity (e.g., inwhich the camera lens 262 is arranged) against intrusion of moisture 210into the cavity. The intrusion of moisture 210 and other foreignsubstances into the cavity can facilitate condensation inside the lenscover system that can obstruct the camera's view. Moisture inside thelens cover system can also damage the controller circuitry 274electronics and/or the pixels (e.g., pixel cells) of the photodetector272. The cavity extends inwards from the lens element 220 to a proximal(e.g., lower) portion of the housing 240.

The cavity is also formed by the camera base 264, which is coupled to(or formed as part of) the housing 240. The camera base 264 can includea photodetector 272 and controller circuitry 274. The photodetector 272can be a video detector for generating electronic images (e.g., videostreams) in response the focused light coupled through the lens element220 and the camera lens (which can include lenses). The controllercircuitry 274 can include: (a) a printed circuit board; (b) circuitry ofthe transducer controller 138; and (c) and the circuitry of thetemperature calculator 140 for controlling the lens cover system 132(e.g., where such circuitry and the lens cover system are arranged in afeedback loop structure). The controller circuitry 274 is coupled toexternal power, control, and information systems using wiring and/oroptical conduits (such as fibers).

The transducer 250 is mechanically coupled to the lens element 220. Thetransducer 250 can be affixed to the lens element 220 by an interveningadhesive layer (e.g., a high-temperature resistant epoxy). In operation,the transducer 250 is arranged to vibrate (e.g., at a selectedfrequency) the lens element 220 in response to transducer driversignals. The transducer driver signals are controllably modulated, suchthat the transducer 250 is controllably excited in response to thetransducer driver signals. The transducer driver signals can beamplitude modulated, such that vibrating lens element 220 cancontrollably expel moisture 210 such foreign material from the externalsurface of the lens element 220 (e.g., external to the cavity).

A lens cover system 200 can include the transducer 250, the housing 240,the seal 230, and the lens element 220. The temperature of the lenscover system can be estimated in response to (e.g., as a function of)electrical properties of the lens cover system. The transducer 250 canbe controllably excited in response to the estimated temperature toefficiently remove obscuring foreign material (including potentiallyobscuring foreign material) from the lens element 220 without exceedinga threshold temperature limit. The transducer 250 can be destroyed ordegraded when operated for prolonged periods at excessively elevatedtemperatures.

The impedance response of the lens cover system 200 varies according tothe temperature of the lens cover system 200. As described herein, therelationship between the estimated temperature of the lens cover system200 and the measured electrical impedance of the lens cover system issubstantially linear within a frequency range. FIG. 3 shows an impedanceresponse of an example lens cover system over a frequency range ofselected temperatures.

FIG. 3 is a waveform diagram of an impedance response of an example lenscover system over a broad frequency range. The waveform diagram 300includes a lens cover system impedance response 310. The lens coversystem impedance response 310 shows the impedance in Ohms over afrequency range between 10 kHz to around 1 MHz. The example lens coversystem can be a lens cover system such as the transducer 250 describedhereinabove.

The “zeros” of the impedance response correspond to the series resonanceproperties, which correspond to the electromechanical vibrationproperties (such as resonance) of a lens cover system that includes theexample transducer. The electromechanical resonances of the system occurat frequencies in which relatively larger vibration amplitudes occur fora variable electrical input amplitude stimulus. For example,electromechanical resonances occur at frequency ranges 321, 322, and323. The zeros are indicated by valleys (such as valley 301) in thecurve 310. A reduced frequency range (e.g., for a “zoomed in” view) ofthe impedance response 310 is described hereinbelow with respect to FIG.4.

FIG. 4 is a waveform diagram of an impedance response of an example lenscover system over a reduced frequency range. The waveform diagram 400includes an example lens cover system impedance response 410. The lenscover system impedance response 410 shows the impedance response of theexample lens cover system over a reduced frequency range (e.g., withrespect to the frequency range shown in FIG. 3).

The lens cover system impedance response 410 includes discretetemperature curves for indicating the lens cover system impedance at adiscrete temperature selected from a range of temperatures. The range ofselected discrete temperatures extends from a temperature of 40° C. to atemperature of −(minus) 60° C., where the temperature represented byeach temperature curve differs from the represented temperature of anadjacent temperature curve by 20° C. The range of temperaturesencompasses operating temperatures potentially encountered in operationof the example lens cover system in various example applications.

For example, the temperature curve 412 shows the example lens coversystem impedance response in Ohms over a frequency range of around 20kHz to 40 kHz at a temperature of −40° C., whereas the temperature curve414 shows the lens cover system impedance response in Ohms over afrequency range of around 20 kHz to 40 kHz at a temperature of −60° C.The lens cover system impedance response 410 includes a valley 401,which indicates a resonance of the example lens cover system at around29 kHz for all illustrated temperature responses.

At frequencies below 150 kHz (e.g., as shown by the lens cover systemimpedance response 310), the gain of an impedance response generallydecreases as the temperature increases, such that the lens cover systemimpedance response 410 is inversely related to temperature within aselected operating frequency range (e.g., with exceptions occurringaround the locations of resonant frequencies of the example transducer).The change in the impedance over temperature is linear (e.g., having aconstant slope and having a change in impedance that is proportional toa step change in temperature).

For example, the vertical spacing (e.g., for a given frequency) betweeneach temperature curve between temperature curves 412 and 414 of aselected operating frequency is equal (e.g., substantially equal). Theselected operating frequency is selected from a frequency included in alinear response region, such as the linear response region extendingbetween, at least, 20 kHz and 25 kHz). The equal spacing of thetemperature curves between temperature curves 412 and 414 is indicativeof a linear relationship between an operating temperature and a measuredimpedance at a selected operating frequency.

The temperature of the example transducer can be determined in responseto a measurement of the impedance of the example transducer. Forexample, the example transducer is excited to vibration (e.g., inresponse to amplitude-modulated driver signals) at a frequency of afrequency range in which the change in the transducer impedance overfrequency is linear.

The dependent variable temperature T as a function of the impedancevariable Z for the example transducer is expressed as the linearequation:

T=−0.29*Z+392.6  (1)

which has a coefficient of determination R² value of R²=0.9932 (e.g.,which is substantially linear, and wherein the constant “−0.29” is aslope of the linear equation, and the constant “392.6” is a y-interceptof the linear equation). The dependent variable temperature T as afunction of the impedance variable Z for the example transducer can alsobe expressed as the parabolic equation:

T=A*Z ² +B*Z+C  (2)

where A, B and C are constants. When A=0, Equation (2) is reduced to thelinear form (such as the form of Equation (1)). Accordingly, theselected operating frequency is selected from within a frequency regionwithin which the relationship between the estimated temperature and themeasured impedance is determinable as a quadratic function (e.g.,according to the Equation (2)).

The determined relationship between the estimated temperature of thelens cover system and the actual (e.g., empirically measured)temperature of the example lens cover system is substantially linearwhen the coefficient of determination R² value is at least 0.95, forexample. As the value of the coefficient of determination R² approachesunity, the statistical variance between an estimated value using thelinear equation and the actual value is minimized. As the value ofcoefficient of determination recedes from unity, errors in theestimation increase, which can result in any of: (a) decreasedtemperature operating range; (b) increased safety margins; and (c)decreased life of the lens cover system.

FIG. 5 is a plot diagram showing a linear relationship between theimpedance response of an example lens cover system and operatingtemperatures thereof while operating at a selected operating frequencyof 20 kHz. The operating temperature of a lens cover system can beestimated by measuring the impedance of the lens cover system at aselected operating frequency, and by converting the impedancemeasurement to an estimated temperature (e.g., according to therelationship described by Equation (1) hereinabove). The conversion ofthe impedance measurement to an estimated temperature can be executed inresponse to calculating the Equation (1) result, and/or by indexing alookup table to retrieve a result according to Equation (1).

Plot 500 shows the close statistical correlation between estimated curve520 (EST) and a corresponding empirically measured curve 510 (MEAS). Theactual (e.g., simulation value of) temperature is shown by theempirically measured curve 510. The estimated temperature (e.g.,calculated using Equation (1)) is shown by the estimated curve 520. Theestimated curve 520 can be estimated in simulations by controlling thetemperature (e.g., from −60° C. to 40° C.) to derive impedancemeasurements (e.g., ranging from around 1150 Ohms to 1475 ohms) of theexample lens cover system. The empirically measured curve 510 and theestimated curve 520 are statistically correlated to a high degree.

As shown by the plot 500, the relationship between the estimatedtemperature of the lens cover system and the actual (e.g., empiricallymeasured) temperature of the example lens cover system is linear (e.g.,substantially linear). The maximum error (e.g., determined insimulations between corresponding points of the estimated curve 520 andthe empirically measured curve 510) shown by plot 500 is 3.7° C.Accordingly, the lens cover system temperature can be accuratelyestimated using a simple linear equation.

For example, a temperature error 3.7° C. of a temperature estimate issufficiently accurate, such that the example lens cover system can besafely operated when the transducer controller maintains the estimatedoperating temperature of the example lens cover system below atemperature threshold for estimated temperatures. As describedhereinbelow, the operating temperature threshold for estimatedtemperatures can be selected in response to the error margin of theestimated temperature measurement and the Curie temperature of theexample transducer. The Curie temperature can be a temperature thresholdbeyond which the permanent polarization of piezoelectric materials ofthe example transducer is degraded. Accordingly, the temperaturethreshold is for delineating (e.g., an upper limit of) an operatingtemperature range below which the example transducer can be activatedwithout (e.g., accelerated) depolarization.

In an embodiment, the impedance data over a range of temperatures for aselected operating frequency can be measured at discrete temperaturesand stored as a lookup table in memory (e.g., which reduces processingrequirements for calculating the equation otherwise calculated todetermine an instant operating temperature). Simple (e.g.,one-dimensional) linear interpolation can be used to more preciselydetermine the operating temperature (e.g., depending on a particularapplication of the described techniques, such as measuring a temperatureoutside a vehicle for determining a control decision describedhereinbelow).

In an embodiment, impedance data measured over a range of temperaturesand over a range of operating frequencies can be stored. The impedancedata can be measured at discrete temperatures and discrete operatingfrequencies and stored as a lookup table in memory (e.g., such thatfirmware would not have to be programmed for controlling specifictransducers, each of which can be operated mutually differentfrequencies according to a selected transducer and a selectedapplication). Simple (e.g., two-dimensional) linear interpolation can beused to more precisely determine the operating temperature for aselected operating frequency.

FIG. 6 is a flow diagram of an example process for estimating atemperature of an example lens cover system in response to an impedancemeasurement of the example lens cover system. The flow 600 can beperformed by hardware circuits exclusive of programming commands. Forexample, the example process can be executed by apparatus includinganalog and/or digital control circuits (such as registers, adders,multipliers, voltage generators, and comparators) that are arranged(e.g., pipelined) according to the process 600, described hereinbelow.

The flow 600 begins at operation 610, in which an example transducer isactivated (e.g., electrically excited to resonance at a selectedfrequency by assertion of amplitude-modulated transducer driversignals). For example, the amplitude-modulated transducer driver signalsare asserted to effect a resonance of the example lens cover system atthe selected frequency of 20 kHz (which is a frequency at which a linearrelationship exists between the temperature of the example lens coversystem and the impedance of the lens cover system). The flow continuesto operation 620.

At operation 620, the impedance (e.g., effective impedance) of theactivated example lens cover system is measured. The impedance can bemeasured in response to a voltage drop resulting from coupling theexample transducer to the asserted amplitude-modulated transducer driversignals, for example. Because the example lens cover system is excitedto resonate at 20 kHz, the measured impedance is derived in response tothe example transducer resonating at the selected frequency of 20 kHz.The flow continues to operation 630.

At operation 630, the measured impedance is converted to an estimatedtemperature. The estimated temperature is determined according to thelinear relationship between the impedance of the example lens coversystem and the operating temperature of the example lens cover system.For example, the measured impedance can be converted to the estimatedtemperature by circuits operating according to the function of Equation(1), and/or the measured impedance can be converted to the estimatedtemperature in response to indexing a lookup table with values forcreating the output of Equation (1). The lookup table includesaddressable values that can be addressed using the independent variable(e.g., the measured impedance) as the index, and that are output asresults for providing or determining the value of the dependentvariable. For example, the addressable values are determined (e.g.,pre-calculated before or after deployment of the system 100) accordingto Equation (1). The flow continues to operation 640.

At operation 640, the temperature is compared against a temperaturethreshold. The temperature threshold can be determined in response tothe Curie temperature and a safety margin. The safety margin can beselected in response to the Curie temperature, the maximum expectederror of the estimated lens cover system temperature, and a margin for“derating” the lens cover system for increasing product lifetime (e.g.,increasing the mean-time-between-failure reliability factor) of theexample lens cover system. The flow continues to operation 650.

At operation 650, the activation state of the transducer is toggled(e.g., activated when the example transducer is in a deactivated state,or is deactivated when the example transducer is in an activated state)in response to the comparison at operation 640. For example, the exampletransducer is deactivated if the temperature indicates that the examplelens cover system has an operating temperature that approaches aself-damaging temperature. The example transducer can be deactivatedwhen the comparison at operation 640 indicates that the estimatedtemperature exceeds half of the Curie temperature (in degrees Celsius)of the example transducer.

The process 600 can be invoked each time the example transducer isactivated. The length of a periodic interval (e.g., fixed period) oftime the example transducer is activated can be limited (for example)for the purpose of periodically re-invoking the process 600, which inturn limits the accumulation of heat from operating the exampletransducer. The example transducer can be deactivated in response to theexpiration of a fixed period of time during which the example transduceris activated. The length of time selected for limiting the activatedtime of the example transducer can be selected in view of the rate ofaccumulation of heat during operation at the selected operatingfrequency and the relative sizes of safety margins. Accordingly, therise of temperature of the example lens cover system is controllablylimited below levels that are likely to permanently (e.g., withoutrepair) damage the example transducer (e.g., without incurring thespace, cost, and reliability considerations otherwise encountered bycoupling a thermocouple to the example transducer).

FIG. 7 is an isometric view of an example camera lens cover system. Thecamera lens cover system 700 generally includes a transducer 710, powerwires 720, a lens element 730 and bonding agent 740. The transducer 710of the camera lens cover system 700 can be a cylindrical transducer suchas transducer 250, described hereinabove, that is arranged to applyultrasonic vibrations for cleaning a camera lens cover.

The transducer 710 is arranged to vibrate a mechanically coupled lenscover (e.g., the lens element 730) in response to being driven by anelectronic amplifier at frequencies ranging from around 20 kHz to 2.0MHz. The transducer 710 can be driven at a given excitation frequencyand a resulting impedance sensed by coupling signals to and from thetransducer via the power wires 720. The resulting impedance can beaffected by temperature, mechanical characteristics, electricalcharacteristics and the frequency at which the transducer is driven, forexample. A lens element 730 is secured to a distal surface of thetransducer 710 by a bonding agent 740 (e.g. epoxy) disposed (e.g., as acircular shape) between the distal surface of the transducer 710 and anadjacent portion of a surface of the lens element 730. The seal betweenthe transducer element and the lens element 730 helps prevent theintrusion of moisture into a sealed cavity (e.g., which can be formed bya camera base, the transducer 710, the lens element 730, and the bondingagent 740).

Environmental moisture (e.g., water drops, water droplets and/or a filmof condensation) can adhere to an exterior surface of the lens element730. The moisture can occlude light from being clearly received by acamera lens in the sealed cavity. The transducer 710 is operable tovibrate at a selected frequency for motivating the dispersal of themoisture (or other foreign materials) from the exterior (e.g., outer)surface of the lens element 730. When droplets of moisture and/or a filmof condensation remain on the exterior surface of the lens element 730,the remaining moisture can cause saturation of the image sensoroptically coupled to the camera lens when, for example, incident lightencounters the exterior surface of the lens element 730 at an obliqueangle.

The exterior surface of the lens element 730 can be formed without a“lip” (or can be formed with a lip arranged with channels extendingtherethrough), which provides a path for moisture migration duringvibration. Vibration of the sealed lens element urges moisture along thepath for moisture migration, for example, because the vibration helpsovercome surface tension of the moisture (which otherwise helps themoisture to adhere to itself as well as to adhere to the outer surfaceof the lens element 730). As described hereinbelow with respect to FIG.8, the transducer 710 is arranged to (e.g., both) vibrate at theselected frequency and to generate thermal energy for heating the lenselement 730.

FIG. 8 is an external view of foreign contaminant volumes for an examplecamera lens cover system. Water drops “contaminate” a lens surface(e.g., of lens element 730), such that a view through the lens surfaceis blocked or otherwise obscured. In an example, a camera lens coversystem is vertically oriented, such that the lens element 730 is level,and such that moisture is not removed by gravity (e.g., for the purposeof illustration) during the moisture removal stages 810, 820, and 830.In the example, the multi-stage cleaning diagram 800 includes alarge-volume cleaning stage 810 (e.g., for generally removing dropsgreater than around 15 μL in volume, such as drop 812), a medium-volumecleaning stage 820 (e.g., for generally removing drops less than around15 μL in volume, such as drop 822), and a small-volume cleaning stage830 (e.g., for removing residual moisture, such as droplets 832).

In the large-volume cleaning stage 810, the transducer is arranged tovibrate in a first mode at a first selected frequency such that waterdrops of around 4-10 mm (or greater) diameter are dispersed (e.g.,atomized or otherwise reduced in size) in response to vibrationgenerated at the first selected frequency. In the first mode (in stage810), a large-volume cleaning excitation signal is applied to thetransducer to generate vibration at the first selected frequency. Thefirst selected frequency can be a frequency in a frequency range atwhich electromechanical resonances occur. The first selected frequencycan be characterized by a relatively high frequency vibration thatconsumes a relatively high amount of power. The large-volume cleaningstage 810 can be followed by the medium-volume cleaning stage 820.

In the medium-volume cleaning stage 820, the transducer is arranged tovibrate in a second mode at a second selected frequency, such that waterdrops (or droplets) of around 1-4 mm diameter are dispersed (e.g.,atomized or otherwise reduced in size) in response to the vibrationgenerated at the second selected frequency. In the second mode (in stage820), a medium-volume cleaning excitation signal is applied to thetransducer to generate vibration at the second selected frequency. Thesecond selected frequency can be a frequency in a frequency range atwhich electromechanical resonances occur. The second selected frequencycan be a frequency that is lower than the first selected frequency. Thefirst selected frequency can be characterized by a relatively lowfrequency vibration that consumes a relatively low amount of power. Themedium-volume cleaning stage 810 can be followed by a small-volumecleaning stage 830.

In the small-volume cleaning stage 830, the transducer is arranged tovibrate in a third mode at a third selected frequency, such that waterdroplets of around 0-1 mm diameter are evaporated (e.g., atomized orotherwise dispersed) in response to the heat and vibration generated atthe third selected frequency. In the third mode (in stage 830), aheating excitation signal is applied to the transducer to generatevibration at the third selected frequency. The third selected frequencycan be a frequency in a frequency range at which electromechanicalresonances occur. The water droplets of around 0-1 mm diameter aredifficult to remove by vibrations because, for example, the surfacetension of the water as well as the relatively high van der Waals forcesexerted between the surface of the lens cover and the water.

The third selected frequency can be a frequency that is higher than thefirst selected frequency. The third selected frequency can becharacterized by a relatively high frequency vibration that consumes arelatively high amount of power. The heat generated by the transducer isthermally coupled to the lens element via the bonding agent 740interposed between the transducer 710 and the lens element 730. The heattransferred to the lens element 730 helps remove any residual droplets,condensates on the lens element.

A control system described hereinbelow with respect to FIG. 9 isarranged to control the amount of heat generated so as to not overheatthe piezoelectric material (which can damage the transducer actuator)and to avoid exceeding safe touch temperatures on the surface of thetransparent element 730. The transducer temperature can be estimated bymeasuring the impedance of the lens cover system as describedhereinabove.

FIG. 9 is a block diagram of an example signal generator of an examplecamera lens cover system. For example, the signal generator 900 isarranged to control signals for driving a transducer of the lens coversystem, to monitor the transducer performance and to change aspects ofthe drive signals in response to the monitored transducer performance.

The signal generator 900 includes a voltage (V) boost circuit 902 thatis arranged to receive power (such as 12 volts direct current input froma vehicle power system) and to generate a 50-volt potential (e.g.,surge-protected potential) from the received 12-volt input power. The50-volt potential is modulated as described hereinbelow for driving atransducer of the camera lens cover system.

The signal generator 900 also includes an embedded core (such as amicrocontroller unit MCU) 910 for executing instructions to transformthe embedded core into a special-purpose machine for executing thefunctions of the camera lens cover system controller 920. For example,the camera lens cover system controller 920 includes control algorithms922, pulse width modulation (PWM) signal generation circuit 924,temperature estimation and regulation circuit 926 and system monitoringand diagnostics circuit 928. Such functions are described hereinbelowwith respect to FIG. 10.

The camera lens cover system controller 920 is arranged to selectoperating parameters (such as modes, cleaning stages, frequencies andoperating temperatures) for the camera lens cover system in response tomonitoring the camera lens cover system transducer and to control thePWM switching controller 930 in response to the selected operatingparameters. For example, the camera lens cover system controller 920 isarranged to control PWM switching times of the PWM switching controller930. The PWM switching controller 930 is arranged to signal the PWMPreDriver 940 in response to the switching times received from the PWMswitching controller 930. The PWM PreDriver 940 generates controlsignals for toggling (e.g., actuating) the switches of the Class Ddriver 950. The Class D Driver 950 is a full-bridge rectifier that isarranged to generate +/−50 volts (e.g., 100 volts peak-to-peak) fordriving the transducer 960. The sense circuitry 970 generate current andvoltage signals for sensing impedance of the camera lens cover systemand transducer 960, which are monitored (e.g., buffered) by thetransducer monitor 980. The monitor signals are coupled via amultiplexer (MUX) 990 to the analog-to-digital converter (ADC) 990 forsampling. The embedded core 910 is arranged to receive the sampledcurrent and voltage signals, to compute (via the camera lens coversystem controller 920) new PWM signaling, to perform temperatureestimation and regulation and to perform system monitoring anddiagnostics as described hereinbelow with respect to FIG. 10.

FIG. 10 is a flow diagram 1000 illustrating an example method of foreigncontaminant removal from an exposed surface of the example camera lenscover system described herein. At 1002, the process begins in the cameralens cover system controller described hereinabove. At 1010, the cameralens cover system controller waits a period of time (e.g., waits for thesystem start signal) before identifying and/or determining the existence(presence) of contaminants at 1014. If the wait duration is not expired,the wait duration is updated at 1012, and the process loops back to1010.

At 1014, after the wait period has expired, a frequency measurementdevice monitors the resonant frequency the example camera lens coversystem to identify (for example) the amount of contaminant disposed onthe exposed surface. For example, the amount of a contaminant can bedetermined in response to a measured frequency response of the cameralens cover system and comparing the measured frequency response to adatabase that includes known frequency responses for given types andamounts for specific contaminants. At 1020, the camera lens cover systemcontroller determines whether a contaminating material exists (ispresent) on the camera lens cover, such that at least one operation forcleaning the camera lens cover is initiated. If “YES,” then at 1028, thetemperature of the example camera lens cover system is determined, andtypes of cleaning are selected in response to the determined temperatureas described hereinbelow. If “NO,” then system checks are performed at1030.

If at 1020 the presence of a material is not indicated (“NO”), then at1030, the process initiates system monitoring and diagnostics tests(e.g., during which the camera lens cover system is self-tested). At1032, a decision is made as to whether to disable the system. Forexample, the determination whether to disable the system can bedetermined in response to the nature of faults diagnosed at 1030, aresponse to a user input and/or a response to whether the power has beenturned off to the system. If the system is to be disabled (“YES”), thenat 1034, the system is shut down. If the system is not to be disabled(“NO”), the process loops back to 1010 and waits for a specifiedduration before the process starts again.

As described hereinabove, at 1028, the temperature of the example cameralens cover system is determined. For example, the temperature of theexample camera lens cover system can be determined in response to (e.g.,as a function of) an operating frequency of an activated transducer asdescribed hereinabove, or by a temperature sensing device (such as anexternally coupled thermocouple). The process continues at 1050, forexample.

If at 1050 the determined temperature is below the freezing point ofwater, then at 1052, the camera lens cover system controller generates aheating signal for a specified duration (e.g., time period). Forexample, the camera lens cover system controller can generate a heatingexcitation signal for warming the camera lens cover system as describedhereinabove by exciting the transducer at a frequency at which thetransducer generates relatively large amounts of heat.

At 1054, the temperature of the example camera lens cover system isdetermined. After the temperature is determined (e.g., after initiationof a heating or cleaning mode), the process continues at 1040, afterwhich the process initiates further operations (described hereinbelow)to ensure, for example, the transducer is operated within a safeoperating region of temperatures.

If at 1056 the type and size of detected contaminating materialindicates the contaminating material is to be reduced in size, then at1058, a cleaning signal is generated for cleaning the example cameralens cover system. For example, the camera lens cover system controllercan select a cleaning mode in response to the size of detectedcontaminating material. The cleaning mode can be selected, such that thecleaning signal can be generated as one of a large-volume cleaningexcitation signal, a medium-volume cleaning excitation signal and asmall-volume cleaning excitation signal. The large-volume cleaningexcitation signal can be generated at a frequency conducive toresonating larger size drops of water (for example), whereas themedium-volume cleaning excitation signal can be generated at a frequencyconducive to resonating medium size drops of water (for example) and thesmall-volume cleaning excitation signal can be generated at a frequencyconducive to heating small droplets of water. After the large-volume ormedium-volume cleaning signal is generated and applied at 1058, theprocess continues at 1054 where the temperature of the example cameralens cover system is determined (e.g., to ensure, the transducer isoperated within a safe operating region of temperatures).

If at 1060, the size of detected contaminating material indicates smalldroplets of water (for example), such that drying is indicated, then at1062, a heating signal is generated for cleaning the example camera lenscover system. For example, the camera lens cover system controller cangenerate a heating signal such that water droplets of around 0-1 mmdiameter are evaporated (e.g., atomized or otherwise dispersed) inresponse to the heat and vibration generated in response to the heatingsignal (e.g., applied at a frequency different from the respectivefrequencies of the applied cleaning signals). After the heating signalis generated and applied at 1062, the process continues at 1054 wherethe temperature of the example camera lens cover system is determined(e.g., to ensure, the transducer is operated within a safe operatingregion of temperatures).

After the temperature is determined (e.g., again) at 1054, the processcontinues at 1040, where a decision is made to determine whether thetemperature of the example camera lens cover system exceeds atemperature threshold. For example, the temperature threshold can behalf of the transducer Curie temperature, such that the transducer iscontrolled to operate within a safe temperature range. If “YES,” theprocess proceeds to disable the applied signal (e.g. heating or cleaningsignal) at 1042. At 1044, cooling of the transducer and/or exposedsurface is initialized (e.g., by entering a delay period during whichthe heating or cleaning signal is disabled, such that additional heat isnot generated). At 1046, the process determines the latest temperature,and in response at 1048, a decision is made to determine whether thetransducer temperature has finished cooling. For example, the decisioncan be made in response to the information determined at 1046, such thatthe temperature can be determined to be below a selected temperaturethreshold. In an example, the temperature threshold can be half of thetransducer Curie temperature, such that the transducer is controlled tooperate within a safe temperature range. In another example, thetemperature threshold can be less than the transducer Curie temperature.If “YES” (e.g., when finished cooling), then at 1048, the process loopsback to 1010. If “NO,” then at 1048, the process loops back to 1046,determines a latest temperature and loops back to 1048 (e.g., foradditional cooling).

If “NO” at 1040 (e.g., when the transducer temperature does not exceedthe temperature threshold), then at 1016, a decision is made todetermine whether the cleaning process is complete. If “YES,” then theprocess starts again at 1010. If “NO” at 1016, then at 1018, thecleaning signal duration is updated and the process loops back to 1020for additional testing and potential cleaning operations.

FIG. 11 is a top view of an example vehicle including example cameralens cover systems. The vehicle 1110 includes a vehicle body thatincludes an interior space sheltered from an exterior environment. Thevehicle 1110 includes at least one camera coupled to the vehicle body,where each camera includes a lens element, where the lens element istransparent and is exposed to the exterior environment. The vehicle alsoincludes at least one apparatus that includes a transducer arranged tovibrate the lens element at a selected operating frequency whenoperating in an activated state.

The vehicle 1110 further includes controller circuitry 1150 coupled tothe vehicle, wherein the controller circuitry 1150 includes a userinterface arranged to receive commands generated in response to anoperator operating the vehicle 1110 from the interior space of thevehicle, wherein the controller circuitry 1150 is arranged to measure animpedance of the apparatus while the transducer is operating at theselected operating frequency, wherein the controller circuitry 1150 isarranged to determine an estimated temperature of the apparatus inresponse to the measured impedance, wherein the controller circuitry1150 is arranged to compare the estimated temperature of the apparatusagainst a temperature threshold for delineating an operating temperaturerange of the apparatus, and wherein the controller circuitry 1150 isarranged to toggle an activation state of the transducer in response tocomparing the estimated temperature of the apparatus against thetemperature threshold. The controller circuitry 1150 can be arranged tomeasure an impedance of the apparatus in response to commands receivedfrom the operator operating the vehicle from the interior space of thevehicle 1110. The controller circuitry 1150 can also arranged to measurean impedance of the apparatus in response to the operator starting thevehicle 1110.

The controller circuitry 1150 includes a display 1160 (which can alsoinclude a touch screen) for displaying a synoptic view 1140 in responseto each video signal of a local view 1430 of a local camera (CAM) 1420.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. A method of foreign contaminant removal from alens system, comprising: receiving a system start signal; determining ifcontaminants are present on an exposed surface of the lens system;determining a first size of the contaminants and the type ofcontaminants; measuring a first temperature of the exposed surface ofthe lens system and comparing the first temperature to a firsttemperature threshold; reducing the size of the contaminants by enablinga transducer to vibrate if the first size is above a first thresholdsize; determining a second size of the contaminants; heating the exposedsurface of the lens system for drying if the second size indicates thatwater droplets remain on the exposed surface of the lens system;measuring a second temperature of the transducer and comparing thesecond temperature to a second temperature threshold; and initializing acooling mode if the second temperature exceeds the second thresholdtemperature.
 2. The method of claim 1, wherein the amount and type ofcontaminant is determined by monitoring a system resonant frequency andcomparing to a database of known frequency responses.
 3. The method ofclaim 1, wherein if the first temperature is below a first temperaturethreshold, a heating signal is generated to heat the exposed surface ofthe lens system.
 4. The method of claim 1, wherein the temperatures aremeasured by measuring an impedance of the transducer and comparing tovalues in a lookup table.
 5. The method of claim 1, wherein reducing thesize of the contaminants includes: a large volume cleaning stage inwhich the transducer is arranged to vibrate in a first mode at a firstfrequency; a medium volume cleaning stage in which the transducer isarranged to vibrate in a second mode at a second frequency; and a smallvolume cleaning stage in which the transducer is arranged to vibrate ina third mode at a third frequency.
 6. The method of claim 5, wherein thesecond frequency is lower than the first frequency.
 7. The method ofclaim 5, wherein the third frequency is higher than the first frequency.8. The method of claim 5, wherein a heating excitation signal is used inthe small volume cleaning stage to transfer heat to the lens system. 9.The method of claim 5, wherein the small volume cleaning stage is usedto evaporate water droplets of approximately 1 mm or less in diameter.10. The method of claim 5, wherein the first frequency, second frequencyand third frequency are within a range of electromechanical resonance ofthe lens system.
 11. The method of claim 1, wherein the second thresholdtemperature is below a Curie temperature of a piezoelectric material ofthe transducer.
 12. The method of claim 1, wherein the second thresholdtemperature is less than half a Curie temperature of a piezoelectricmaterial of the transducer.
 13. A system, comprising: a camera whereinthe camera includes a lens element that is transparent and is exposed tothe exterior environment; a transducer to vibrate the lens element at anoperating frequency when the transducer is in an activated state; andcontroller circuitry including a user interface to receive a commandgenerated by an operator, wherein the controller circuitry is adaptedto: measure an impedance of the transducer while the transducer isoperating at the operating frequency; determine an estimated temperatureof the transducer in response to the measured impedance; compare theestimated temperature against a temperature threshold for delineating anoperating temperature range of the transducer; and toggle an activationstate of the transducer in response to comparing the estimatedtemperature against the temperature threshold.
 15. The system of claim14, wherein the controller circuitry is arranged to measure theimpedance in response to the command.
 16. The system of claim 14,wherein the controller circuitry is arranged to measure the impedance inresponse to power being applied to the system.
 17. The system of claim14, wherein the controller circuitry is arranged to measure theimpedance at periodic intervals.
 18. The system of claim 15, comprisinga display to display a video image from the camera to the operator afterthe transducer has been activated.